User Contributed Notes 3 notes

Note that the 'mtime' field only comes from the DOS-format time that's stored in the zip file, which is only accurate to the nearest 2-seconds. Zip files can store mtime's in multiple, optional fields but PHP's zip library does not retrieve them (nor does it provide API to access the extra fields)

The end result is that you will see timestamps that could be out by one second (if the original timestamp was odd), and won't necessarily match was other unzip programs will show the mtime as.

The CRC returned from this method is a signed number and so can be negative. This isn't how most CRC's are represented and so can cause problems. Another thing to know is that the standerd CRC algorithm used for zip files is CRC32b.

So to put this together lets say that you wanted to extract the first file from a zip and then compare the original CRC with the CRC for the extracted file this is what you would need to do. (proper error checking is omitted for simplicity).

<?php
$zip = new ZipArchive();

$zip->open("myZip.zip");

$stat = $zip->statIndex( 0 );

$name = $stat['name'];

$oldCrc = $stat['crc'];

$zip->extractTo("myPath", $name);

$newCrc = hexdec(hash_file("crc32b", "myPath/" . $name));

// Have to test both cases as the unsigned CRC from within the zip might appear negative as a signed int.
if($newCrc !== $oldCrc && ($oldCrc + 4294967296) !== $newCrc) {
echo "The files don't match!";
}
?>